Groundwater is the source of 99% of the drinking water provided to consumers on Oahu, the major island in the state of Hawaii. However, virtually all approved sources of water on Oahu have been planned for use. As a result, plans for new urban development are currently being delayed for lack of approved water sources. A well to provide drinking water was dug by a private developer in an area of questionable
groundwater quality. This investigation assessed the quality of the groundwater and determined whether sewage effluent, which was discharged into an unlined ditch in the vicinity of the well, had an impact on
the quality of the groundwater. The quality of groundwater from a new well dug near the coastal plain on Oahu was determined by pumping out 1 022 m^3 (270,000 gal) of water over 1.5 days and analyzing nine representative samples. No fecal coliforms (<1/100 ml) and only 1.6 fecal streptococcus/ 100 ml were recovered in the nine samples. Also, no human enteric virus was recovered in the four 0.38-m^3 (l00-gal) samples, an indication that the groundwater was not contaminated with sewage. One and three foot soil percolates collected under the ditch which transported sewage near the well were similarly analyzed and the results indicated that it would be most unlikely for sewage-borne bacteria and viruses in the effluent to percolate through the soil profile to contaminate the groundwater. The groundwater was also analyzed for eleven chemicals. The concentration of total dissolved solids (750 mg/l) was the only
measurement which exceeded the MCL for drinking water, although the concentration of chloride (241 mg/l) closely approximated its MCL. Blending of this groundwater with high quality groundwater is a viable alternative of increasing the volume of potable water required for urban expansion.